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Re: 70cm amps





Hi all
Everyone may have an amplifier horror story. Some amps are better than
others.  I have tried three major brands in the 100 plus watt capacity.
Here are a few usage stories.

RF concepts:
  (model?)  10in	170 out meters
Ran good, plenty of power.
Power meets or exceeds specifications.
Built in SWR overload circuit works most of the time.
Can only tolerate limited abuse.
Fried the finals the first time when I feed the wrong antenna for too
long.
Fried the finals the second time when a friend borrowed the amp and
drove
the 10 watt input with 100 watts.
Overall I was please with the amp (3 years usage) and sold it working to
a friend who
is still using it.  I replced it becaues my radio puts out 25-30 watts. 
And it
is very importatn to make sure you do not over drive your Amp.


TE Systems:
Model? 25-30in, 300-400 output, 2-meters.
No swr protections on the High power models, so you must
be careful.
Blew finals transmitting into the coax with out an antenna.
TE fixed it quickly, I paid for the finals, labor was free.
The heat sink is a little small for the power load, 
so i run a small fan to keep it cool.
I have been using this one extensively for ssb and Mir satellite
operations for over 3 years.  


TE Systems:
Model? 25in, 150 output, 435mc.
This model is very voltage sensitive.
At 14.0 volts i get the full published 170 watts.
However at my normal 13.8 volts the output is aprox 150 watts.
The other models are not as sensitive to input voltage.
The heat sink on the 70cm 170 amp is the same size
as the 2meter 400 watt amp.  So I assume the 2meter
heat sink is too small.  This amp seems to handle normal
QSO without too much heat.
In operation for 3 years, no problems.
I use it for SSTV VSB, SSB and FM satellite.

Mirage:
model? 25 in, 300 out, 2-meters
After carefully checking all antenna connections and 
using the pre-amp to verify the cable connections. 
This amp blew on the first key down.
The problem was caused by a last minute assembly change
to a resistor.  A 10-watt resistor was not in stock, so someone
tied two 5 watt resistors together standing up.  The pig-tail leads
touched the metal case and caused the failure.
Two weeks later a replacement arrived.
this one too, failed on the first key down.
I do not know what caused the second failure, i just
switched to TE systems.

All amps will eventually blow.  Most failures are caused by
bad coax or antenna related problems, or user error.

good luck and becareful.

Miles



"Walls, Jim R" wrote:
 > 
 > Bob - W7LRD asked:
 > 
 > > My recent attempts at AO-10 clearly show I need an amp.  Before I make
 > > out the check, I would like to know what the collective wisdom is on this
 > > subject.  A short note- e-mail direct please.
 > 
 > ----------
 > Then Gary "Joe" Mayfield said:
 > 
 > >     I had very good luck with a T.E. Systems amp.  And I know they
 > > are still available.  Burghardt's here in town has them.
 > 
 > > http://www.burghardt-amateur.com
 > 
 > Just my opinion based on our experiences with TE Systems amps - AVOID THEM
 > LIKE THE PLAGUE!  Our club has the better part of a dozen of them in use on
 > our repeater network (13 repeaters on 220).  To date we have had 100%
 > failures on them.  We could not get TE systems to fix them even on
 > warrantee.  In fact several years ago we had sent two amps in for warrantee
 > repair and after 11 months, they had not even opened the shipping box!  We
 > finally drove over to their facility and picked up the box (still
 > un-opened).  We had a RF design engineer take a look at them and he said
 > that the electrical design was right out of a Motorola Application note
 > (except that they pushed the transistors pretty hard), but the thermal
 > design was horrible.  We have redesigned the thermal design and they are
 > better, but we will NEVER buy another one.
 > Professionally, my employer has a bunch of their amps in a commercial system
 > and have also had a very high failure rate.
 > 
 > 73
 > -------------------------
 > Jim Walls - K6CCC
 > k6ccc@amsat.org
 > http://home.earthlink.net/~k6ccc
 > Mobile Radio Operations
 > Southern California Edison Co.
 > Ofc:  626-302-8515    FAX:  626-302-9999
 > Res:  626-914-4641
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